One type of hand operated machine control requires the operator to grasp a handgrip, which may lie at the top of a joystick, and/or operate control buttons on the handgrip. To prevent accidental operation, as when an object leans against the handgrip, a safety switch is commonly provided that must be continually depressed by the operator to enable operation of the equipment. The operator""s hand becomes fatigued when he has to continually keep a switch depressed. Also, if the machinery will operate when a single safety switch is depressed, then there is a danger that if an object leans against the safety switch that the machine will inadvertently operate. Instead of a mechanical switch that must be depressed, it is possible to provide an electrode at or under the surface of the handle, which senses the presence of an operator""s hand to enable the switch to operate. However, even in that case, an object that leans against the switch, may be sensed as a hand, and enable inadvertent operation of the machinery. A circuit that more reliably sensed the presence of an operator""s hand to enable operation of a machine control, would be of value.
A joystick is commonly biased towards a center, or neutral position, although it can be moved in any one of four directions to control a machine. In many cases, the operator must pivot the joystick in one direction and hold it there for an extended period of time. This can be tiring for the operator. Although detents can be located in a cavity where the lower end of the joystick is pivotally mounted, it is crowded in that area, and it is difficult to retrofit detents or repair damaged detents there. A detent system that was readily accessible for retrofit or replacement of damaged parts, and which provided effective biasing of rugged detents, would be value.
In accordance with one embodiment of the present invention, applicant provides a hand operated machine control which is safe and which avoids tiring of the operator. To assure that an operator""s hand is present, a handgrip of the machine control has two electrodes spaced about the handgrip axis, so that the hand of an operator will normally lie adjacent to both of the electrodes simultaneously during operation. The electrodes can lie below the surface that is grasped by the hand, and a circuit connected to the electrodes senses change in capacitance at the electrodes.
Where the handgrip lies at the top of a joystick, fatigue of the operator is further reduced when the joystick must be continuously held at one pivoted position, by provided detents on the joystick and on the housing. A plurality of housing detents are mounted about the aperture through which a middle portion of the joystick projects, and a plurality of joystick detents are mounted on the joystick. The housing detents are mounted on a top wall of the housing, where they are readily accessible for retrofit and for replacement.
The joystick detents are mounted on a collar that is spring biased downwardly but that can tilt and ride up. When a joystick detent rides over a housing detent, the collar is deflected against the biasing of a coil spring that surrounds the joystick, to provide reliable biasing without requiring a weakened resilient portion of the joystick detents.